1. Field of the Invention
This invention relates to a polymaleimide-containing rubber composition and a tire using a rubber member made of such a rubber composition.
2. Description of Related Art
It is well-known that elastic modulus of a vulcanized rubber composition, particularly dynamic storage modulus (Exe2x80x2) is improved by compounding bismaleimide with a rubber composition because bismaleimide acts as a crosslinking agent or the like in the rubber component. Furthermore, the crosslinking of bismaleimide is thermally stable, so that the heat resistance is simultaneously improved.
To this end, various tire performances are improved by using a bismaleimide-containing rubber composition in rubber member for a tire while utilizing characteristics of such a rubber composition.
For example, when a rubber composition is formed by compounding bismaleimide with styrene-butadiene copolymer rubber (SBR) and applied to a tread for the tire, the steering stability, high-speed durability, high-running performance and heat resistance are improved. And also, when silica is compounded with such a rubber composition, the wet-skid performance and rolling resistance are improved.
When a rubber composition is formed by compounding bismaleimide with natural rubber (NR) and applied to a casing member for the tire, since the elastic modulus is high, this composition acts as a strengthening material and contributes to reduce the weight of the tire, control the heat build-up and improve the rolling resistance, adhesion property between rubber and steel cord and fatigue durability.
However, when a large amount of bismaleimide is compounded, vulcanization reaction is obstructed and a long vulcanizing time is taken and hence the productivity undesirably lowers in a certain case. And also, there is caused an inconvenience that an easiness of bubble formation in rubber is degraded.
It is, therefore, an object of the invention to more improve the elastic modulus without damaging the productivity in order to more improve the tire performances.
Since bismaleimide is industrially expensive, it is difficult to be compounded in a large amount considering a cost of a final product, so that the invention is to attain the improvement of the elastic modulus by compounding a small amount of a maleimide-based compound.
According to the invention, there is the provision of a rubber composition comprising at least one rubber ingredient selected from natural rubber and synthetic rubbers, and a polymaleimide synthesized by reacting at least one of anhydrous maleic acid and anhydrous citraconic acid with methylene polyaniline represented by the following general formula (I): 
wherein n is an integer of 1 or more.
Further, the invention lies in a tire using a rubber member made of the above rubber composition. In this case, a gas to be filled in the tire may be air, nitrogen or the like.